Photographic film with fine grain silver chloride underlayer



3 050 391 PHoTooRArrnc FlLlvi wrrn FINE GRAIN; SILVER CHLORIDE UNDERLAYER Thomas R. Thompson and Robert H. Clark, Binghamton,

N.Y., assignors to General Aniline & Film Corporation,

New York, N.Y., a corporationhf Delaware No Drawing. Filed Dec. 30, 1957,- Ser. No. 705,784

This invention relates to the manufacture of photographic film having improved sensitometric characteristics including speed and gradation. More particularly,

it pertains to a photographic film having two emulsion layers including a novel underlayer emulsion of extreme.

low sensitivity.

In the process most widely used at the present time for the manufacture of photographic filrnsof. high sensitivity tude. This arrangement of layers results in an extendedstraight line portion of the density-log exposure curve into the region of higher densities, but does not increase the over-all speed. It is important to note that the lower. density range of speed of the top layer emulsion isnot increased by the slower underlayer emulsion. Thus, the

conventional practice of layer arrangements does not increase the sensitivity of the most sensitive element I It is accordingly an object of this invention to provide a two-layer film having improved photographic charac; teristics. Other objects will be apparent from the fol:

lowing description.

We have found that the speed of a two emulsion layer film is substantially increased by replacing the conventional lower layer by a novel undercoating consisting of a very fine grain, very slow speed emulsion. Thephotographic effect of the bottom layer is such as to increase the speed and gradient of the top layer.

In carrying out the invention, there is first coated upon the film base support a very slow speed emulsion. This slow speed emulsion is composed of a gelatin suspension of very small silver halide crystals having an average or median diameter. on the order of 50 millimicrons. Even thelargest particles do not exceed one micron in diameter as evidenced by the fapt that all particles are invisible under the light microscope even when viewed under the highest'ma gnification. Best results are obtained when thesilver halide is essentially silver chloride. Since the crystals are smallin: size, there altorded a very great surface area of silver halide for a given weight of silver halide since many minute crystals have, a much larger surface than a few largecrystals The small size of the crystals together with their large total surface area and their composition play an im: portant part in this process. Thus, when a high speed bromoiodide silver halide emulsion, of the negative type,

is coated over the slow speed emulsion, a photographic sensitometric evaluation gives a result of higher speed and gradient when compared to a single layer coating of the same high speed emulsion or when compared with a double layer film with two silver halide emulsion coatings in which the relative speeds of the lower and upper layers are essentially of the same magnitude.

The speed of the slow speed underlayer may be so slow that it requires an exposure of from 50 to 2000 times that of the more sensitive top layer. Assuming that the top layer has a relative speed of 100.0 (expressed in terms of reciprocal meter candle second-to develop Z a density of 0.2), the lower layers may have a speed between the range of 0.05 to 2.0. Thus, in this process, the bottom layer contains no developed silver even under conditions of exposure and development which give a highdensity in the top layer. This elfect is clearly demonstrated by the examination under a microscope of cross sections made from a typical step tablet exposure suitably processed. Thus, a step of high density, as at the shoulder of the characteristic curve, shows a dense deposit of silver in the top layer, while the lower layer has no silver, This result is quite different from conventional commercial two layer films in which. much silver density in both-lay ers is observed in cross sections of exposed and'develop'ed high density areas. In this latter case, the purpose "of" the underlayer is to contribute density at higher exposure levels, thus extending the latitude of the product. In our invention, the underlayer contributes no density by virtue of developed silver in the underlayer itself.

The presence of the special underlayer of our invention does result in more silver density in the top layer after exposure and processing. A full scientific explanation of the mechanism by which our invention operates is not yet known. However, general considerations lead to two explanations, it being understood, of course, tha t difiuseinto the-top layerand supports a sub latent image;

intensification.

alternate theory postulates that aftercoatlng, the silver chloride of the bottom layer absorbs bromideions:

from the top layer. It is known that highly sensitive silver bromoiodide emulsions contain solublebromide ions which serve to stabilize the emulsion against fog or sensitivity changes during the film manufacture including the emulsion coating operation, .OIICB the emulsionis coated on the support and Waterremoved by drying, the; bromide concentration increases. The high concentrations of bromide in the dried filmrtnay well reduce the film speed or reducenthe development rate or increase the induction period of development. I a

It is now. assumed by us that when the sensitive top layer is over-coated upon the fine grain, low speedsilver chloride undercoating, soluble bromide ions maydiffuse from the top layer and be adsorbed by the silver chloride.

Thev adsorptionof bromide ions by particles, of'silver" chloride is essentially a surface reacti'om Therefore, the

greater "surface of silver chloride afforded by the'small; particle size will promote a greater amount of bromide ion removal. Since bromide'ions can dilfusejthroughout gelatin layers while silver chloride particles do not diffuse,

there is reason to believe that at equilibriumthe bromide ion concentration of the'toplayer can be reduced. The evidence available sofar has not fully proven that'eitherof the theories is correct, and it is, therefore, not intended; that the scope of our invention be limited bythe foregoing postulations.

The preferred type of undercoating emulsion is a silver chloride emulsion. A very slow speed silver chloride. emulsion which is washed free of excess salts and has. submicroscopic silver chloride particles within the size-I. range specificis needed-for that purpose. Since light sensitivity is not a factor, the silver chloride emulsion. does not require a second digestion (after ripening); Ordinary photographic gelatins such as gelatin made from; bone .or hide are satisfactory. Silver bromide-and silver bromoiodide emulsions can not be used. When theyare- 7 silver halide.

erocyclic derivatives such as Z-mercaptobenzothiazole. or Z-mercapto-5-phenyltetrazole when added to the undercoating drastically reduce or even eliminate the speed effect.

The silver chloride undercoating is most efiective in. causing speed and gradient increases in a medium or high speed silver bromoiodide overcoating. If overcoatings are used which have the speed of positive emulsions, little or no efiect is observed. For this reason,-an overcoating must be selected which belongs to the category of a high speed ammonia or boiled type emulsion of the type in which the silver halide in predominately silver bromide or silver bromoiodide with the iodide concentration not exceeding 5 mole percent based on the total weight of The top layer may be optically sensitized and may, if desired, contain color formers fast to diffusion.

A wide variety of commercially available developers including those which are known by their trade names: Ansco 47, Ansco Permadol or Ansco Liquadol can be used satisfactorily for the development of our new materials. These developers are used for black and white development and contain hydroquinone and p-methylaminophenol (Metol) as the developing agents. Their composition is illustrated by Ansco A-47 which has the following formula:

Water to make 1.0 liter.

Modifications in the composition of the developer, for

instance, by adding excessive amounts of potassium examples, although it is to be understood that the invention is not to be restricted thereto.

EXAMPLE I Silver Chloride Emulsion Part IA:

Water milliliters 225 Sodium chloride grams 25.5

Gelatin dn 16.5 Part IB:

- Water milliliters 225 Sodium chloride grams.. 19.65 Part II:

Water milliliters" 650 Silver nitrate grams 60 Solutions IB and II were added simultaneously during the course of two minutes to solution LA with agitation at a temperature of 52 C. After a five minute period of digestion at 52 C., the mixture was precipitated by the addition of 90 grams of ammonium sulfate. Stirring was stopped and the precipitated silver'chloride gelatin particles allowed to settle. Excess salts were removed by washing with decantation using dilution ratio of 1 to 4 and a total of three washes, After the final decantation, the precipitate was reconstituted with 75 grams of gelatin dissolved in 600 milliliters of water by agitating at 50 for twenty minutes. The resulting. emulsion was made up to 1200 milliliters with water. and found to have a pAg of 6.6p-and a pH of 5.7, 7 H

The silver chloride emulsion was coated on a subbed cellulose acetate support to athickness of 7 microns and, after drying, was overcoated with a medium speed silver bromoiodide emulsion at a thickness of 14 microns. A

Grams Metol I 1.5 Sodium sulfite, anhydrous 45.0 Sodium bisulfite 3.0

Hydroquinone 6.0 7 Sodium carbonate, monohydrated 6.0 Potassium bromide 0.8

control coating was prepared by coating the silver bromm iodide emulsion directly on the subbed support.

After a sensitometric exposure and processing, including 3 minute development in Ansco Liquadol, fixing and washing, the following speed (l/e at density 0.2), gradient and fog values were obtained.

Fog Speed Gradient Control 0. 07 Test; 0. 08

V Fog i Speed Gradient EXAMPLE III Using the same silver chloride undercoat of Example I, an overcoating was prepared using a high speed silver bromoiodide emulsion at a thickness of 15 microns.

Fog Speed Gradient Control 0.01 0. 99

Test 0. 08 142 1. s5

EXAMPLE IV As in Example III, a high speed silver bromoiodide emulsion was coated on a silver chloride emulsion undercoat. However, a polyethyleneoxide oleyl ether accelerator was added to the silver bromoiodide emulsion overcoating in the amount of 0.5 gram per liter of emulsion. The test coatings and the controls were developed for four minutes in Ansco Permadol.

Part II was added during the course of one minute to part I at a temperature of 50". After digesting for fifteen minutes, the mixture was chilled, shredded and washed to a conductivtiy of twentyx 10- mho.

The silver chloride emulsion was coated on a film base support at a thickness of 7 microns and overcoated with a high speed silver bromoiodide emulsion of the ammonia type. After a sensitometric exposure and after process-' ing one set of strips with AnscofLiquadol developer for three minutes, and the other set of strips with Ansco 47 developer for eight minutes, the following data was obtained.

Development Fog Speed Gradient 3 Liquadol-. 0.12 1.27 3 Liquad0l" 17 1. 33

It will be seen from the above examples that the silver chloride underlayer emulsion is prepared in' a simple manner. Other silver chloride emulsions, prepared by difierent procedures, may be used instead. In any case, the scientist skilled in the art can suitably adjust coating weights and amount of ingredients to achieve optimum results, provided the silver chloride particles are kept small in size for best results. The type of emulsion employed for the overcoating is not considered to be unusual. However, medium or high speed silver bromoiodide emulsion containing from 1 to 5 mole percent iodide either of neutral or of the ammonium type are preferred.

Still other modifications of the invention will occur to persons skilled in the art. We, therefore, do not intend to be limited in the patent granted except as necessitated by-the appended claims.

We claim:

1. A light-sensitive material carrying on a plastic transparent support in the following order, a subbing layer, a slow speed gelatinous silver chloride emulsion layer in which the silver chloride particles are of submicro scopic size and have a median particle size on the order of 50 millimicrons, and in direct contact with said silver chloride emulsion layer, a permanent high-speed gelatinous silver halide emulsion layer in which the silver halide emulsion is selected from the group consisting of silver bromide and silver bromoiodide emulsions and has a relative speed ranging from 45 to 138, the relative speed of said high-speed silver halide emulsion exceedring that of said silver chloride emulsion by a factor ranging irom 50 to 2000, the speed of said lower silver chloride layer being so slow that no silver image is formed therein under conditions of exposure black and white development and fixing which give .a high density silver image in the top layer, saidrelative speed being expressed in terms of reciprocal candle seconds to develop a density of 0.2.

2. In the process of forming a negative silver image in an imagewise exposed silver halide material, said process including the steps of black and white developing, fixing, washing and drying said silver halide material to form a permanent negative image therein, the improvement which consists of using as the light sensitive material a photographic element carrying on a plastic transparent support in the following order, a subbing layer, a slow-speed gelatin silver chloride emulsion layer in which the silver chloride particles are of subrnicroscopic size and have an average particle size of less than 50 millimicrons, and in integral contiguous contact with said silver chloride emulsion layer, a high-speed gelatin silver halide emulsion layer in which the silver halide emulsion is selected from the group consisting of silver bromide and silver bromoiodide emulsions, the photo- 5 graphic etfects of said improvement "being such as to increase the effective speed and gradient of the silver image in the silver halide emulsion layer without the formation of a silver image in the silver chloride emulsion layer.

3. In the process of forming a negative silver image in an imagewise exposed silver halide material, said process including the steps of black and white developing, fixing, washing and drying said silver halide material to form a permanent negative image therein, the improvement which consists of using as the light sensitive material 'a. photographic element on a subbed transparent plastic support a gelatin silver bromoiodide emulsion layer having a relative speed ranging from 45 to 138 and between said emulsion layer and said support and in direct contact with said emulsion layer, a silver chloride gelatin emulsion layer in which the silver gelatin chloride particles are of submicroscopic size and have a median particle size of less than 50 mil'limicrons, said silver chloride emulsion having :a relative speed between the range of 0.03 to 2.7, the speed of said silver chloride emulsion being insuflicient to have a visible image formed therein under conditions of exposure and black and white development which give a high density silver image in said high-speed bromoiodide emulsion, said relative speed being expressed in terms of reciprocal candle seconds to develop a density of 0.2, the photographic effects of said improvement being such as to increase the eifective speed and gradient of the silver image in the silver halide emulsion layer without the formation of a silver image in the silver chloride emulsion layer.

4. A process as defined by claim 2 wherein said silver halide emulsion layer contains a polyethyleneoxide oleyl ether accelerator.

5. A process :as defined by claim 3 wherein said silver halide emulsion layer contains a polyethyleneoxide oleyl ether accelerator.

References Cited in the file of this patent UNITED STATES PATENTS 1,303,635 Capstafl s May 13, 1919 2,202,026 Renwick May 28, 1940 2,231,684 Schinzel Feb. 11, 1941 2,258,187 Mannes et a1. Oct. 7, 1941 2,312,543 Goldfinger Mar. 2, 1943 2,712,995 Weyde July 12, 1955 2,725,296 Kendall Nov. 29, 1955 2,927,024 Woodward et a1. Mar. 1, 1960 FOREIGN PATENTS 912,605 France June 14, 1946 OTHER REFERENCES Mees: The Theory of the Photographic Process, pages 23 and 178, Macmillan Co., NY. (1954). 

1. A LIGHT-SENSITIVE MATERIAL CARRYING ON A PLASTIC TRANSPARENT SUPPORT IN THE FOLLOWING ORDER, A SUBBING LAYER, A SLOW SPEED GELATINOUS SILVER CHLORIDE EMULSION LAYER IN WHICH THE SILVER CHLORIDE PARTICLES ARE OF SUBMICROSCOPIC SIZE AND HAVE A MEDIAN PARTICLE SIZE ON THE ORDER OF 50 MILLIMICRONS, AND IN DIRECT CONTACT WITH SAID SILVER CHLORIDE EMULSION LAYER, APERMANENT HIGH-SPEED GELATINOUS SILVER HALIDE EMULSION LAYER IN WHICH THE SILVER HALIDE EMULSION IS SELECTED FROM THE GROUP CONSISTING OF SILVER BROMIDE AND SILVER BROMOIODIDE EMULSIONS AND HAS A RELATIVE SPEED RANGING FROM 45 TO 138, THE RELATIVE SPEED OF SAID HIGH-SPEED SILVER HALIDE EMULSION EXCEEDING THAT OF SAID SILVER CHLORIDE EMULSION BY A FACTOR RANGING FROM 50 TO 2000, THE SPEED OF SAID LOWER SILVER CHLORIDE LAYER BEING SO SLOW THAT NO SILVER IMAGE IS FORMED THEREIN UNDER CONDITIONS OF EXPOSURE BLACK AND WHITE DEVELOPMENT AND FIXING WHICH GIVE A HIGH DENSITY SILVER IMAGE IN THE TOP LAYER, SAID RELATIVE SPEED BEING EXPRESSED IN TERMS OF RECIPROCAL CANDLE SECONDS TO DEVELOP A DENSITY OF 0.2. 